Engineering Conferences International ECI Digital Archives Nonstoichiometric Compounds VI Proceedings 9-7-2016 Detection and relevance of ion conduction in hybrid organic-inorganic halide perovskites for photovoltaic applications Alessandro Senocrate Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany ; École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland, a.senocrate@fkf.mpg.de Tae-Youl Yang Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany Giuliano Gregori Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany Norman Pellet École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland; Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany Michael Grätzel École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland; Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany See next page for additional authors Follow this and additional works at: http://dc.engconfintl.org/nonstoichiometric_vi Recommended Citation Alessandro Senocrate, Tae-Youl Yang, Giuliano Gregori, Norman Pellet, Michael Grätzel, and Joachim Maier, "Detection and relevance of ion conduction in hybrid organic-inorganic halide perovskites for photovoltaic applications" in "Nonstoichiometric Compounds VI", ECI Symposium Series, (2016). http://dc.engconfintl.org/nonstoichiometric_vi/27 This Abstract and Presentation is brought to you for free and open access by the Proceedings at ECI Digital Archives. It has been accepted for inclusion in Nonstoichiometric Compounds VI by an authorized administrator of ECI Digital Archives. For more information, please contact franco@bepress.com.
Authors Alessandro Senocrate, Tae-Youl Yang, Giuliano Gregori, Norman Pellet, Michael Grätzel, and Joachim Maier This abstract and presentation is available at ECI Digital Archives: http://dc.engconfintl.org/nonstoichiometric_vi/27
Detection and relevance of ion conduction in CH 3 NH 3 PbI 3 for photovoltaic applications Alessandro Senocrate, Tae-Youl Yang, Giuliano Gregori, Gee Yeong Kim, Michael Grätzel and Joachim Maier Non Stoichiometric Compound VI Santa Fe (NM) 5-8 Sept. 2016 a.senocrate@fkf.mpg.de 1 / 15
CH3 NH3 PbI3 and Perovskite Solar Cells Introduction Results Conclusions Eames et al., Nat. Commun., 2015 Direct EG = 1.5 ev High absorption Low exciton bind. energy :100 µm diffusion lenghts1 High PCE of > 22 %2 1 Dong et al., Science, 2015, 347, 967-970. Li et al., Nature Chem., 2015 Anomalous behaviours Degradation (T, P(H2 O)) Low stability of devices Low reproducibility 2 NREL National Center for Photovoltaics. 2 / 15
Why study ion migration in CH 3 NH 3 PbI 3? 1 Expected concentration of ionic defect is high 2 Ionic defects related to stability 3 It can explains "anomalous" low frequency behaviours 4 Ionic defects influence on photovoltaic properties Hysteresis in i-v sweeps Large dielectric polarisation Unger et al., Energy & Environ. Sci., 2014 Juarez-Perez, J. Phys. Chem. Lett., 2014 3 / 15
Outline 1 Evidences of ionic transport in CH 3 NH 3 PbI 3 : DC-galvanostatic polarisation EMF measurements 2 Identification of the mobile defects: Conductivity as f(exchangeable components) Chemical modifications (doping) 3 Concluding remarks 4 / 15
Stoichiometric polarisation of CH 3 NH 3 PbI 3 Extracted values: σ ion = 7.7 10 9 S cm 1 σ eon = 1.9 10 9 S cm 1 D δ = 2.4 10 8 cm 2 s 1 Without Bias With Bias Yang et al., Angew. Chemie Int. Ed. 2015 5 / 15
Stoichiometric polarisation of CH 3 NH 3 PbI 3 CH 3 NH 3 PbI 3 is a mixed conductor with σ ion > σ eon in dark conditions. Extracted values: σ ion = 7.7 10 9 S cm 1 σ eon = 1.9 10 9 S cm 1 D δ = 2.4 10 8 cm 2 s 1 Since µ ion << µ eon, we expect ionic defects dominating. 5 / 15
EMF measurements V OC = t ion f G (PbI2 ) 2 f G (CuI/AgI) 2F EMF experiments show a clear ionic contribution. t ion values in agreement with DC-galvanostatic data. 6 / 15
Identification of the moving ion 10 na, in Ar, 50 C, 1 week + Pb MAPbI 3 AgI Ag - A B C D E I - MA + Ag+ Pb 2+ Further characterisations: EDS and XRD confirmed the presence of PbI 2 on the interface B. Yang et al., Angew. Chemie Int. Ed. 2015 We can conclude that: Iodine is the moving ion in CH 3 NH 3 PbI 3. 7 / 15
Kröger-Vink diagrams Defect chemistry reactions: 1) 1 I 2 2 + V I I x I + h K 1 = [h ] [V I ]P1 / 2 I 2 2) 1 I 2 2 + MA MA x V MA + h + MAI K 2 = [V MA ][h ] P 1 / 2 I 2 3) MAI V I + V MA K S = [V MA ][V I ] 4) 0 h + e K I = [e ][h ] Assumptions: Vacancies are more easily formed 1 2 No Pb defects (high H f and E A ) 3 4 I i found in literature with low E A 5 [1] Walsh et al., Angew. Chemie Int. Ed., 2015, 54, 1791. [2] Kim et al., J. Phys. Chem. Lett., 2015, 5, 1312. [3] Eames et al., Nat. Commun., 2015, 6, 7497. [4] Azpiroz et al., Energy Environ. Sci., 2015, 8, 2118. [5] Haruyama et al., J. Am. Chem. Soc., 2015, 137, 10048. 8 / 15
Pure CH 3 NH 3 PbI 3 : I 2 partial pressure l o g ( c o n d u c t i v i t y / S c m - 1 ) 7 0 C, A r, d a r k - 4, h i g h t o l o w P ( I 2 ) - 5-6 - 7-8 - 9 0. 5 7-0. 1 8 s i o n s e o n - 7-6 - 5-4 l o g ( P ( I 2 ) / a t m ) Pure MAPI P(I 2 ) : Semi-quantitative agreement σ eon is p-type V I is the mobile defect. 9 / 15
Pure CH3 NH3 PbI3 : I2 partial pressure - 4-5 - 6-7 - 8-9, 7 0 C, h i g h / ( c o n d u c t i v i t y l o g A r, t o Results l o w P ( I 2) s - 0. 1 8-7 l o g - 6 ( P ( I 2) s / Conclusions d a r k 0. 5 7 S c m - 1 ) Introduction e o n i o n - 5 a t m ) - 4 Pure MAPI P(I2 ) : Semi-quantitative agreement σeon is p-type VI is the mobile defect. 9 / 15
Na-doped CH 3 NH 3 PbI 3 l o g ( c o n d u c t i v i t y / S c m - 1 ) - 6. 5-7. 0-7. 5 T = 7 0 C P ( I 2 ) = - 6. 7 a t m P ( O 2 ) = - 4. 3 a t m 1 % a t. N a N o m i n a l N a c o n t e n t s e o n s i o n P u r e l o g [ d e f e c t s ] A ', V I P l o g [ A ' ] V M A ', V I h A ' I D e ' N l o g [ D ] D, V M A ' Na Pb compensated by V I and h σ eon and σ ion increase with doping Doping concentration is only nominal! 10 / 15
Na-doped CH 3 NH 3 PbI 3 : P(I 2 ) l o g ( c o n d u c t i v i t y / S c m - 1 ) - 4 7 0 C, A r, d a r k, h i g h t o l o w P ( I 2 ) - 5-6 - 7 0. 5 6 s e o n s i o n - 7-6 - 5-4 l o g ( P ( I 2 ) / a t m ) l o g [ d e f e c t s ] A ', V I h V M A ' e ' - 1 / 2 A I 1 / 2 1 / 2 A ', h A I I l o g P ( I 2 ) - 1 / 2 V M A ', h V I P 1 / 4-1 / 4 CH 3 NH 3 Na 0.01 Pb 0.99 I 2.99 : No decrease in σ ion Significant increase in σ eon V I is the mobile defect. 11 / 15
Pure CH 3 NH 3 PbI 3 : O 2 partial pressure l o g ( c o n d u c t i v i t y / S c m - 1 ) - 6-7 - 8 7 0 C, A r, d a r k, h i g h t o l o w P ( O 2 ) 0. 1 6 s e o n - 0. 0 5 s i o n - 9-5 - 4-3 - 2-1 0 l o g ( P ( O 2 ) / a t m ) l o g [ d e f e c t s ] 1 / 4 V M A ', V I 1 / 4 h O - 1 / 4 I ' 1 / 2 e ' - 1 / 4 I O l o g P ( O 2 ) O I ', V I A r, d a r k, P ( I 2 ) = - 5. 3 a t m l o g ( c o n d u c t i v i t y / S c m - 1 ) - 6-7 - 8-9, 7 0 C, 1 C s e o n s i o n - 5-4 - 3-2 - 1 0 l o g ( P ( O 2 ) / a t m ) Pure MAPbI 3 P(O 2 ) : O 2 effect only in absence of I 2. O 2 can change I 2 activity over sample (surface reaction). 12 / 15
Conductivity equilibration: I 2 and O 2 C o n d u c t i v i t y / S c m - 1 2. 0 x - 6 1. 8 x - 6 1. 6 x - 6 P ( I 2 ) f r o m - 6. 8 t o - 6. 1 a t m τ δ = 1 5 0 0 m i n σ e o n E x p. f i t 0 2 0 0 0 4 0 0 0 6 0 0 0 8 0 0 0 0 0 0 T i m e / m i n C o n d u c t i v i t y / S c m - 1-5 P ( O 2 ) f r o m 7 x - 8 6 x - 8 5 x - 8 4 x - 8 3 x - 8 2 x - 8 t δ = 3 5 m i n t o - 3 a t m 1 x - 8 0 5 0 0 1 5 0 2 0 0 T i m e / m i n σ e o n E x p. f i t O 2 exposure has fast equilibration. I 2 equilibration is 40x slower. Surface nature of O 2 interaction. 13 / 15
Concluding remarks: 1 CH 3 NH 3 PbI 3 is p-type electronic conductor. 2 I is the mobile ion and V I are mobile defects. 3 O 2 appears to only affect I 2 activity. 4 Electrical properties can be significantly tuned. Effect of I 2, O 2 treatments under light has yet to be investigated. 14 / 15
Thanks Thank you for your kind attention! Acknowledgments: Florian Kaiser Dr. Rotraut Merkle 15 / 15